Corrosion Tests at the Water Treatment Plant in Jakubany / Korózne Skúšky Na Úpravní Vody Jakubany

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Corrosion Tests at the Water Treatment Plant in Jakubany / Korózne Skúšky Na Úpravní Vody Jakubany

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  51 GeoScience Engineering Volume LX (2014), No.4 http://gse.vsb.cz p. 51-60, ISSN 1802-5420 CORROSION TESTS AT THE WATER TREATMENT PLANT IN JAKUBANY KOR ÓZNE SKÚŠKY NA ÚPRAVNÍ VODY JAKUBANY    MATÚŠ GALÍK    1  , JOZEF KRIŠ    2  , JÁN ILAVSKÝ 3   1  Ing. Matúš Galík   , Faculty of Civil Engineering, Slovak University of Technology,  Radlinskeho 11, 813 68 Bratislava, Slovak Republic, tel. (+421)59 274 274 matus.galik@stuba.sk 2  prof. Ing. Jozef Kriš, PhD.  , Faculty of Civil Engineering, Slovak University of Technology,  Radlinskeho 11, 813 68 Bratislava, Slovak Republic, tel. (+421)59 274 615  jozef.kris@stuba.sk 3   doc. Ing. Ján Ilavský, PhD., Faculty of Civil Engineering, Slovak University of Technology,  Radlinskeho 11, 813 68 Bratislava, Slovak Republic, tel. (+421)59 274 609  jan.ilavsky@stuba.sk Abstract External corrosion, which depends on environmental and operating conditions, is the main cause of structural deterioration of all metallic mains. Internal corrosion, on the other hand, can cause significant functional (hydraulic, water quality) deterioration within a distribution system. This work deals with the corrosion of water pipes which greatly affects the durability and failure rate of water systems. The test is evaluated in accordance with STN 75 7151 and ASTM D2688-11. The corrosion tests were carried out on raw and treated water at the water treatment plant in Jakubany. Abstrakt Hlavnou príčinou poškodenia konštrukcie všetkých kovových sietí je vonkajšia korózia, ktorá je závislá od prostr edie a prevádzkových podmienok  . V nútorná korózia môže spôsobiť významné funkčné zhoršenie (hydra ulické, kvalita vody)   v rámci distribučného systému. Táto práca sa zaoberá koróziou vodovodného  potrubia, ktorá   výrazne ovplyvňuje odolnosť  vodovod ných systémov. Skúška je hodnotená v súlade s  STN 75 7151 a ASTM D2688-11 . Korózne testy boli vykonané na surovej a upravenej vode na úpravní  vody Jakubany. Key words:  The corrosion, water treatment, incrustations, change in water quality 1   INTRODUCTION A water supply system represents a complex mechanism which is affected by many factors. In terms of economy, it is also an exacting system whose service life is limited by the durability of used materials. The durability of materials has a significant impact on reliability of water supply systems and on the quality of supplied water for human consumption. The majority of water supply systems were built in past when increasing water consumption was assumed. Therefore, the water supply systems are overdesigned. By decreasing the water consumption in overdesigned water supply systems, the extension of water retention period occurs and it may negatively affect the sensorial character of supplied water as well as result in microbial contamination. The interaction between water and pipeline materials occurs during the transport of water in water supply network, which may lead to a decrease in water quality (Vreeburg 2007) [1]. Water supply operators (companies) often deal with this problem in water supply systems which consist of metal pipelines. In water supply systems, corrosion processes occur which have a negative impact on water quality (Munka 2005) [2]. The corrosion is mainly caused by electrochemical processes which are formed at the water and pipe material interface. The basis of all these reactions consists in oxidation-reduction (redox) reactions which lead to the degradation and depreciation of material (Slavíčková, 2006 ) [3]. Lytle et al. [4] found that metal levels rapidly increased with respect to stagnation time. High flow velocities can assist the formation of protective coatings by diffusing effectively protective ingredients to the metal surface. However, high flow velocities can mechanically remove the protective wall coating and pipe material, resulting in erosion corrosion or impingement attack. High flow velocities increase the rate, at which dissolved oxygen comes into contact with pipe surfaces, which can affect corrosion rates due to the involvement  52 GeoScience Engineering Volume LX (2014), No.4 http://gse.vsb.cz p. 51-60, ISSN 1802-5420 of oxygen in the corrosion chemical reactions. Volk et al. [5] and Fang et al. [6] studied the effect of temperature on the corrosion of iron in water and clearly demonstrated that the corrosion increased as a function of temperature. Many other authors who monitored the course of processes corrosive to water pipes made of iron came to the conclusion that corrosion is a major cause of colour changes in water piping [7],[8].   The negative effects of corrosion are mainly expressed by:    Decreasing the water quality (by its secondary ferrization, decreasing the content of solved oxygen, leaching of lead, zinc, copper and other substances from armature into water),    Deterioration of hydraulic conditions of water flow    Reduction of pipeline service life    Increase in number of disorders and water decrements of pipeline    Increasing costs of water pumping (Singley et al, 1984) [9]. The corrosion of pipeline has a significant impact on water supply system reliability. Specifically, it is  just a reliable and sustained drinking water supply system which represents the basic requirement for social and economic development of a certain area. Corrosion costs encountered in the water distribution division included expenditure for replacing aging infrastructure, lost water from unaccounted-for leaks, corrosion inhibitors, internal mortar linings, external coatings, and cathodic protection (Devietti 2011) [10]. This study aimed at quantifying key water quality parameters, such as flow velocity, pH, biofilm growth, temperature, and evaluating the influence of these parameters on corrosion and iron release in a drinking water distribution system. The test is evaluated in accordance with STN 75 7151 and ASTM D2688-11. The corrosion tests were carried out on raw and treated waters at the water treatment plant in Jakubany. 2   WATER AGRESIVITY DETERMINATION It is possible to determine whether the water has corrosive effects or not by using chemical water analyses through a direct CaCO 3  test, by means of various calculations or corrosion tests. Determining the water aggressivity based on chemical analyses represents some advantages, such as a relatively quick way of obtaining results, possibility of periodical testing, which means regular control of water quality. The changes in water quality and the results of the tests can be compared. On the other hand, the water aggressivity calculations count only the water agsressivity that is caused by aggressive CO 2 , which represents a disadvantage described by many authors. No calculation takes into account the amount of dissolved oxygen in water or the velocity of flowing water which may represent two dominating factors in influencing the corrosion progress significantly. The method for the corrosion test is mentioned in the standard STN 75 7151 “ Requirements for quality of water in piping systems ”  [11] and is based on measuring differences in mass decrease of tested samples on the 30 th  and 60 th  day after their exposition to the effects of flowing water. For the tests, 42x42 mm coupons with a thickness of 1 mm are used. From the obtained results of corrosion decrement, corrosion velocities are calculated. The velocities show the reduction in pipe wall thickness. If it is necessary to determine the corrosion type in addition to the corrosion decrement, the time period of the test is prolonged to one year. The advantage of this test lies in the effect of water on testing samples which is as complex as the effect of water on the pipeline. The impact of dissolved oxygen in water may occur and be denoted as the dominating factor causing the corrosion or as the positive factor causing the passivation of metal by forming a layer with a good protective properties which separates the transported water from the  pipeline surface (Dubová et al, 2010)  [12]. From the decrement of testing coupons, the corrosion velocity was determined according to the formulas of STN 75 7151: Average corrosion decrement (g.m -2 ) is calculated as an arithmetic average of 5 testing coupons fixed in one coupon holder according to the following formula: K  ´= 1 1  nii K n     ( 1)  The calculation of corrosion decrements of particular samples in g · m -2 : K=  1 2 m ms    (2 )    53 GeoScience Engineering Volume LX (2014), No.4 http://gse.vsb.cz p. 51-60, ISSN 1802-5420 Where: m 1    –   weight before exposition 2 gm     , m 2    –   sample weight after exposition 2 gm     , S     –   sample surface [m 2 ]. The calculation of corrosion decrements, U t , in µm during exposition :   U  t    =    1.7.86 K K    (3 )  Where: K   - average of corrosion decrements of 5 samples 2 gm     ,  K´   - decrement of sample during the blank sample test, which is performed for controlling the possibility of testing samples dissolution in removal process of corrosion waste products in HCL, 2 gm     , 7.86 - specific weight of steel 3 gcm     , The calculation of corrosion velocity, v u , in µm in 1 year time period: v u   = 2 1 2 1 365.( ) t t  U U t t    (4 )  Where: t  1    –   shorter exposition time of sample [d], t  2    –   longer exposition time of sample [d], Ut  1    –   corrosion decrement of sampl e in shorter exposition time [µm],   Ut  2  - corrosion decrement of sample in longer exposition time [µm].  Based on the corrosion test results obtained between the 30 th  and 60 th  day, the water is classified by the aggressivity level depending on the corrosion velocity in µm for 1 year   as shown in Tab. 1. Tab. 1 Water aggressivity level classification according to corrosion velocity [11]. Aggressivity level Corrosion velocity v t   [µm.year  -1 ] Classification I   <50 moderately aggressive II 50 until 150 medium aggressive III >150 strongly aggressive The water is classified according to the aggressivity levels into three following categories: I.   No anti-corrosion precaution required II.   Considered individually; the decision about anti-corrosion actions is made with regard to required pipeline service life and based on the results of technical and economic analyses III.   Anti-corrosion actions must be provided with regard to required pipeline service life As the next equipment for classification of aggressive properties of transported water, an ASTM D2688-11 [13] device was used, in which the testing coupons were installed. The coupon size was 74x9 mm and the thickness 1 mm. The corrosion velocity was calculated according to the following relations. The calculation of corrosion decrements of particular samples in mg: W   = i f  W W    (5 )    54 GeoScience Engineering Volume LX (2014), No.4 http://gse.vsb.cz p. 51-60, ISSN 1802-5420 Where: W  i    –   sample weight before exposition [mg], W   f     –   sample weight after exposition [mg]. The obtained weight values are put into the calculation of corrosion velocity: KR  = . m factor t    (6 )  Where: Δ m    –   determined decrement of weight [mg], Δ  t     –   onset period of coupon [day], factor  –   0.025 (for steel of class 11). 3   CORROSION TEST AT THE WTP JAKUBANY The corrosion tests were performed in cooperation with the company PVPS, a.s. (Podta transká Water Oper  ating Company) at the water treatment plant (WTP) in Jakubany, a village in the Stará Ľubovňa  District (Fig. 1). Raw water for treatment is sampled directly from the Jakubianka brook and is transported by gravity through a DN 500 pipeline to the water treatment plant. The treatment plant is capable to produce 150 liters per second. Currently, the production is about 60 liters per second. The water treatment technology at the Jakubany treatment plant varies according to season. Over the winter, the brook water quality is at a very high level and the detritus tank is weaned because of ice-cover formation and the only treatment of water by using pressure filters is provided. Fig. 1 WTP in Jakubany. The treatment process at the WTP in Jakubany is chosen with regard to the quality of water input. Therefore, the processes used at the WTP in Jakubany include mechanical precleaning, simple sedimentation and consequent 1-step coagulative filtration which is used only in case of impaired raw water quality. In case of need, aluminium sulphate, a coagulation reagent, is added to pressure mixing tanks and the consequently formed flocks are removed by means of pressure sand filters. Health safety of filtered water is ensured by gaseous chlorine, or by chloramination, which is accumulated in a tank with a capacity of 2500 m 3 . The water is transported from the tank through gravity pipes to the consumption area. This work consists in long-time monitoring of corrosion in the water supply pipeline. Measurements were performed from 11 th  May 2013 to 12 th  May 2014. Two devices for monitoring the corrosion velocity were used in order to make the operational classification of aggressive character of water. Testing coupons (according to STN) were used for tests performed on one of the devices and coupons according to ASTM were used for the tests on the other one. These devices were placed into a raw water intake location of the WTP, downstream the pressure filters and upstream the disinfection (Fig. 2).  55 GeoScience Engineering Volume LX (2014), No.4 http://gse.vsb.cz p. 51-60, ISSN 1802-5420 Fig. 2 Technological scheme of WTP in Jakubany   A  –   Jakubianka water source, B  –   draining of settled sludge, C  –   aluminium sulphate dosing, D  –   water disinfection, E  –   conduit to water storage, U1,H1  –   corrosion equipment according to STN, U2, H2  –   corrosion equipment according to ASTM, 1  –   sampling object, 2  –   sedimentation tank, 3  –   pressure mixing tank, 4  –   pressure sand filter, 5  –   accumulation tank The water quality was monitored also during the change of testing coupons in corrosion devices. In terms of chemical changes, the quality of water at the WTP in Jakubany did not change significantly. The quality values were: pH 7.22-8.32, temperate 0.2  –   17 o C, KNK 4,5 1.4-2.2 mmol.l -1 , ZNK4,5 below 0.06 mmol.l -1 , Fe 0.008-0.067 mg. l -1 , Mn below 0.01 mg. l -1 , Ca 2+  28.1-40.5 mg.l -1 . Turbidness of raw water was observed in a range of 0.00-1.60 ZF. Fig. 3 shows the temperature progress during the measurement. The average year temperature was 7.6 °C.   Fig. 3 Water temperature progress in a period of 11.5.2013 - 12.5.2014 4   RESULTS 4.1 Results according to STN From the performed measurements, it is obvious that the progress of corrosion velocities of raw water and treated water is a bit different. Fig. 4 shows the consideration of corrosion velocities between 30 and 60 days of measuring. Due to these standardized results, the water is classified into I and II aggressivity levels. During the first two tests (5/13 and 6/13), the corrosion velocity of raw water showed a higher value as it was in case of using the water that passed the treatment process. This was probably induced by a water flow decrease (down to stopping) through the corrosion equipment, which was caused by strong storm-related turbidity. During the 5 th  and 9 th  tests, the corrosion velocity also increased.   In case of seven tests, the corrosion velocity of water that passed the treatment process was higher than the velocity of raw water which might be caused by a higher flowing velocity, disinfection reagent (gaseous chlorine), using which the pre-disinfection before the filter is provided, or which might be caused by coagulant (aluminium sulphate).
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